A DC distribution network anti-islanding detection method, system and control method thereof

Abstract

The present invention relates to an anti-islanding detection method, system and control method of a DC distribution network. The detection method of the present invention adopts a total of three levels of discrimination to determine whether the DC distribution network is in an islanding operation state, and starts anti-islanding protection according to a set threshold value. The method has the characteristics of short detection time, high detection result accuracy and reliability, and can quickly start anti-islanding protection.

Description

Technical Field

[0001] The present invention belongs to the technical field of direct current distribution networks, and in particular relates to an anti-islanding detection method, system and control method of a direct current distribution network. Background Art

[0002] As traditional fossil energy is becoming increasingly depleted, global climate change and environmental pollution are becoming increasingly serious. In order to meet the growing energy demand of human society and reduce the environmental burden, it is urgent to develop clean, low-carbon, sustainable green energy. Therefore, distributed photovoltaic power generation in distributed power sources is an effective form of solar energy utilization with high conversion efficiency, which is conducive to full utilization of resources and improves the reliability of energy supply.

[0003] The DC distribution network is one of the new directions for the development of the distribution network in the future. In recent years, it has received extensive attention from the academic community and has been put into use in demonstration projects. One of the advantages of the DC distribution network is its flexibility and openness. It eliminates the inverter link for the access of DC power sources such as photovoltaic power generation, greatly reduces the cost of distributed power generation access to the grid, and can adapt to the large-scale access of distributed power sources. However, similar to AC access, there are technical problems in preventing the islanding effect when distributed photovoltaic power generation is connected to the DC distribution network.

[0004] DC distribution network islanding means that after the DC distribution network trips due to a fault or maintenance, the DG system at the user end fails to detect the power outage in time and disconnects itself from the main system, forming a self-sufficient power supply island consisting of the DG (Distributed Generation, DG for short) system and the surrounding DC loads. Island operation can be divided into unplanned island operation and planned island operation. Unplanned islanding refers to the state in which the distributed generation is the only power source to supply power to the load when the power grid loses power. Planned island operation is an artificial island operation, which can reduce the losses caused by power outages and improve reliability. The unpredictable characteristics of unplanned islands will seriously affect the safe operation of the power system.

[0005] The hazards caused by the island effect include: the stability of power supply and power quality in the island cannot be guaranteed, the island is electrified and affects the low-voltage reclosing switch, the island is electrified during maintenance and threatens the safety of personnel and equipment, and power supply rights and responsibilities are prone to disputes. The anti-islanding of DC distribution network is different from that of AC power grid. It cannot detect frequency anomalies and cannot implement active frequency shift to avoid blind spots, making it more difficult to prevent islanding.

[0006] Physical quantities such as voltage and current in the DC distribution network are DC signals, which do not contain frequency and phase information. The AC system detection method based on changes in parameters such as AC signal phase, frequency, and reactive power cannot be applied in the DC distribution network.

[0007] Therefore, it is an urgent problem for technical personnel in this field to provide an anti-islanding method and a control method for a DC distribution network that can solve the above-mentioned technical problems, and can timely and accurately detect whether an islanding phenomenon occurs in a distributed power source. When an islanding phenomenon occurs, the distributed power source is promptly controlled to stop operating. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide an anti-islanding detection method, system and control method for a DC distribution network, which can timely and accurately detect whether an islanding phenomenon occurs in a distributed power source, and when an islanding phenomenon occurs, timely control the distributed power source to stop running.

[0009] The technical solution adopted by the present invention is:

[0010] A method for detecting an anti-islanding of a DC distribution network comprises: sampling an inverter output current and a voltage at a PCC point; comparing the voltage at the PCC point with a set first threshold value: if the voltage at the PCC point satisfies the first threshold value, it is determined that the power supply mode is an islanding power supply mode; otherwise, detection is performed using wavelet packet energy entropy and a BP neural network according to the inverter output current and the voltage signal at the PCC point; if the power supply mode is determined to be an islanding power supply mode, an islanding power supply control strategy is selected for execution; otherwise, an AC voltage component is injected into an output end of an AC / DC interface converter, and a voltage signal at an output end of a DC / DC converter is sampled to obtain an effective value of an AC signal; and the effective value of the AC signal is compared with a third threshold value: if the effective value of the AC signal is less than a preset voltage value, it is determined that the power supply mode is an islanding power supply mode; otherwise, it is determined that no islanding occurs.

[0011] Furthermore, the first threshold value includes an upper voltage limit U max And the voltage lower limit U min ; If the voltage U at the PCC point satisfies: U>U max Or U<U min , then the power supply mode is determined to be the island power supply mode, and the island power supply control strategy is selected to be executed; U min ≤U≤U max , by collecting and decomposing the inverter output current and the voltage signal at the PCC point, the concept of information entropy is introduced, and the information entropy and wavelet packet decomposition are combined to obtain the feature vector.

[0012] Furthermore, the third threshold is a preset voltage value U set , if the effective value of the AC signal U' satisfies: U' set , it is determined that the power supply mode is the island power supply mode, and the island power supply control strategy is selected to be executed; if U'>Uset, it is determined that the island does not occur, the power supply mode is the mains network system power supply mode, and the mains network system power supply control strategy is selected to be executed. ​

[0013] Furthermore, the island detection step using wavelet packet energy entropy and BP neural network according to the inverter output current and the voltage signal at the PCC point includes: controlling it with an algorithm combining wavelet packet decomposition and information entropy, collecting and decomposing the inverter output current and the voltage signal at the PCC point, introducing the concept of information entropy, combining information entropy and wavelet packet decomposition to obtain a feature vector; normalizing the feature vector to obtain a 6-dimensional vector as the input of the BP neural network, training and learning in the hidden layer, and finally making an island judgment through the output layer; if it is determined that the power supply mode is an island power supply mode, selecting to execute the island power supply control strategy; if it is determined that the island does not occur, the power supply mode is the mains network system power supply mode, and selecting to execute the mains network system power supply control strategy.

[0014] Furthermore, when the DC distribution network is a two-terminal distribution network, it includes two AC / DC interface converters, namely a first AC / DC interface converter and a second AC / DC interface converter; the first AC system is connected to the DC distribution network through the first AC / DC interface converter, and the second AC system is connected to the DC distribution network through the second AC / DC interface converter.

[0015] Furthermore, an AC voltage component is injected into the output end of the interface converter, specifically including: if it is determined that both interface converters are working normally, then an AC voltage component is injected into the output end of any one of the AC / DC interface converters; if it is determined that one of the two interface converters fails, then an AC voltage component is injected into the output end of an AC / DC interface converter that is working normally.

[0016] Furthermore, the method for determining whether an AC / DC interface converter has a fault is as follows: sampling a second voltage signal at the output end of the AC / DC interface converter; extracting a second effective value of the AC signal in the second voltage signal; comparing the second effective value with a second preset voltage value; and determining that the AC / DC interface converter has a fault when the second effective value is less than the second preset voltage value.

[0017] Furthermore, the injected AC voltage component u ac * The expression of u is as follows: ac * =kU dc sin(2πf ac t); where U dc is the rated DC voltage of the DC distribution network; k is the percentage of the injected AC voltage component; f ac is the frequency of the AC voltage component; the value range of k is 2-5%; f acIt is 10-60% of the power frequency; the first preset voltage value and the second preset voltage value are the same, both are Uset, and the value range of Uset is 5-20% of kUdc.

[0018] A DC distribution network anti-islanding detection system, comprising a mains network subsystem, other power supplies, a distributed power supply 1, a distributed power supply 2, and a load; the mains network subsystem comprises a first mains power grid system and a second mains power grid system, the first mains power grid system comprises a first power supply G1, a first AC power supply circuit breaker CB11, a first AC transformer T1, a first AC line circuit breaker CB12, a first voltage source converter, and a first DC line circuit breaker CB13 connected in sequence through a distribution line; the second mains power grid system comprises a second backup power supply G2, a second AC power supply circuit breaker CB21, a second AC transformer T2, a second AC line circuit breaker CB22, a second voltage source converter, and a second DC line circuit breaker CB23 connected in sequence through a distribution line;

[0019] The output end of the first AC power circuit breaker CB11 is connected to the output end of the second AC power circuit breaker CB21 through a DC circuit breaker CB7, and the output end of the first AC transformer T1 is connected to the output end of the second AC transformer T2 through a DC circuit breaker CB8; the first DC circuit breaker CB13 is connected to other power sources, distributed power source 1, distributed power source 2 and loads respectively; the second DC circuit breaker CB23 is connected to other power sources, distributed power source 1, distributed power source 2 and loads respectively; the load is also connected to the other power sources, distributed power source 1 and distributed power source 2 respectively;

[0020] The other power sources include a first branch DC circuit breaker CB1 connected in sequence through a distribution line; the other end of the first branch DC circuit breaker CB1 is respectively connected to the first DC line breaker CB13, the second DC line breaker CB23 and the second branch DC circuit breaker CB2; the distributed power source 1 includes a fourth branch DC converter and a fourth branch DC circuit breaker CB4; one end of the fourth branch DC circuit breaker CB4 is connected to the fourth branch DC converter and the third branch DC circuit breaker CB3 through a distribution line, The other end of the fourth branch DC circuit breaker CB4 is connected to the first DC circuit breaker CB13 and the second DC circuit breaker CB23 respectively; the distributed power source 2 includes a sixth branch DC circuit breaker CB6 and a sixth branch DC converter; one end of the sixth branch DC circuit breaker CB6 is connected to the sixth branch DC converter and the fifth branch DC circuit breaker CB5 through a distribution line; the other end of the sixth branch DC circuit breaker CB6 is connected to the first DC circuit breaker CB13 and the second DC circuit breaker CB2 3 connection; the load includes other DC loads, local DC load 1 and local DC load 2, the other DC load includes the second branch DC circuit breaker CB2; one end of the second branch DC circuit breaker CB2 is connected to other DC loads through a distribution line; the other end of the second branch DC circuit breaker CB2 is respectively connected to the first DC circuit breaker CB13, the second DC circuit breaker CB23 and the first branch DC circuit breaker CB1; the local DC load 1 includes the third branch DC circuit breaker CB3; the first One end of the 3-branch DC circuit breaker CB3 is connected to the local DC load 1 through a distribution line, and the other end of the 3-branch DC circuit breaker CB3 is respectively connected to the 4-branch DC circuit breaker CB4 and the 4-branch DC converter; the local DC load 2 includes the 5th branch DC circuit breaker CB5; one end of the 5th branch DC circuit breaker CB5 is connected to the local DC load 2 through a distribution line, and the other end of the 5th branch DC circuit breaker CB5 is respectively connected to the 6th branch DC circuit breaker CB6 and the 6th branch DC converter.

[0021] A method for preventing islanding in a DC power distribution network comprises the following steps:

[0022] Step 1: Determine whether an island occurs;

[0023] Step 2: If it is determined that islanding does not occur, the power supply mode is the mains power network system power supply mode, and the mains power network system power supply control strategy is selected to be executed;

[0024] Step 3: If it is determined that an island occurs and the power supply mode is an island power supply mode, an island power supply control strategy is selected to be executed;

[0025] The power supply control strategy of the mains network system includes: when executing the power supply control strategy of the mains network system, judging whether the first mains network subsystem is operating normally; when the first mains network system is operating normally, controlling the first mains network system to supply power; if the first mains network system fails, detecting the fault location, adjusting the power supply path according to the fault location, so as to avoid the fault location for power supply, including: (1) if it is detected that the fault location is located from the first power supply G1 to the first AC power supply circuit breaker CB11, triggering the first AC power supply circuit breaker CB11 to disconnect, the seventh branch DC circuit breaker CB7 to connect, and controlling the second backup power supply G2 to connect to the first mains network system for power supply; (2) if it is detected that the fault location is located from the first AC power supply circuit breaker CB11 to the first AC line breaker CB12, the first AC line breaker CB12 is triggered to disconnect, the eighth branch DC breaker CB8 is triggered to connect, and the first power supply G1 is controlled to connect to the second mains power grid system for power supply; (3) If the fault location is detected between the first AC power supply breaker CB11 and the first AC line breaker CB12, the first AC power supply breaker is triggered to disconnect CB11, and the second mains power grid system is controlled to supply power; (4) If the fault location is detected between the first AC line breaker CB12 and the first DC line breaker CB13, the first AC line breaker CB12 is triggered to disconnect, the eighth branch DC breaker CB8 is connected, and the first power supply G1 is controlled to connect to the second mains power grid system for power supply;

[0026] The power supply control strategy of the mains power network system also includes: if the first mains power grid system fails, controlling the distributed power source 1, the distributed power source 2 and other power sources to supply power to the load until the adjustment of the power supply path is completed;

[0027] The island power supply control strategy includes: detecting whether the total power of distributed power source 1, distributed power source 2 and other power sources meets the load demand; if so, controlling distributed power source 1, distributed power source 2 and other power sources to supply power to the load; if not, controlling distributed power source 1, distributed power source 2 and other power sources to supply power to the satisfied load.

[0028] The positive effects of the present invention are: the detection method adopts a total of three levels of discrimination to determine whether the DC distribution network is in an island operation state, and starts the anti-island protection according to the set threshold value, which has the characteristics of short detection time, high accuracy and reliability of detection results, and can quickly start the anti-island protection. The detection system includes a city power network subsystem, other power supplies, distributed power supply 1, distributed power supply 2, and load; the load is also connected to the other power supplies, distributed power supply 1, and distributed power supply 2 respectively; and the supporting distribution system overcomes the shortcomings of the traditional single power grid power supply mode and multiple conversion links, low efficiency, and high failure rate, with diverse line selections and reliable signal transmission, which can reduce the number of equipment and transmission losses and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 It is a schematic diagram of the system structure of the present invention. DETAILED DESCRIPTION

[0031] Example 1

[0032] As attached Figure 2 The figure shows a schematic diagram of the anti-islanding system structure of a DC distribution network. When no islanding occurs, the DC voltage of the DC distribution network is very stable under the control of the AC / DC converter and DC / DC converter of the first municipal power grid system, with relatively small fluctuations, and the voltage at the PCC point remains basically stable. Once an islanding occurs, the voltage amplitude, change rate, fluctuation, etc. will change. At this time, there are two types of islanding situations:

[0033] 1) In case 1, power generation and load reach a new balance point, forming a relatively stable island state. In the new state, the DC voltage value of the PCC point will be significantly higher or lower than the normal voltage range. Whether it is in the island operation state can be determined based on the voltage value;

[0034] 2) Case 2: When the power matching degree between the distributed power source and the load in the island is high, the voltage amplitude of the PCC point is within the normal voltage range. However, due to the location dispersion and power randomness of the distributed power source, the voltage fluctuation amplitude of the PCC point will also exceed the normal range. At this time, the output current of the inverter and the voltage signal at the PCC point are collected and decomposed, and the concept of information entropy is introduced to combine information entropy and wavelet packet decomposition to obtain the feature vector; the feature vector is normalized to obtain a 6-dimensional vector as the input of the BP neural network, which is trained and learned in the hidden layer, and finally the island is judged through the output layer.

[0035] Case three, if an island occurs other than in the first two cases and still cannot be identified, the AC voltage component (frequency is less than the industrial frequency) can be injected into the output end of the AC / DC interface converter, and then the voltage signal at the output end of the DC / DC converter can be sampled to obtain the effective value of the AC signal; the effective value of the AC signal is compared with the third threshold (preset voltage value): if the effective value of the AC signal is less than the preset voltage value, it is determined that the power supply mode is the island power supply mode, and the island power supply control strategy is executed; if the effective value of the AC signal is greater than the preset voltage value, it is determined that the island does not occur.

[0036] Example 2

[0037] As attached Figure 1 As shown, this embodiment provides an anti-islanding method for a DC distribution network and a control method thereof, including: sampling the inverter output current and the voltage at the PCC point; comparing the voltage at the PCC point with a set first threshold: if the voltage at the PCC point meets the first threshold, it is determined that the power supply mode is an islanding power supply mode, and the islanding power supply control strategy is selected to be executed; if the voltage at the PCC point does not meet the first threshold, the inverter output current and the voltage signal at the PCC point are collected and decomposed, and the concept of information entropy is introduced to combine information entropy and wavelet packet decomposition to obtain a feature vector; the feature vector is normalized to obtain a 6-dimensional vector as the input of the BP neural network, and training and learning are performed in the hidden layer, and the optimal Finally, the islanding judgment is performed through the output layer; if the power supply mode is determined to be the islanding power supply mode, the islanding power supply control strategy is selected to be executed; if it is determined that the islanding does not occur, the AC voltage component (frequency is less than the power frequency) is injected into the output end of the AC / DC interface converter, and then the voltage signal at the output end of the DC / DC converter is sampled to obtain the effective value of the AC signal; the effective value of the AC signal is compared with the third threshold (preset voltage value): if the effective value of the AC signal is less than the preset voltage value, the power supply mode is determined to be the islanding power supply mode, and the islanding power supply control strategy is selected to be executed; if the effective value of the AC signal is greater than the preset voltage value, it is determined that the islanding does not occur, the power supply mode is the mains network system power supply mode, and the mains network system power supply control strategy is selected to be executed. By sampling the inverter output current and the voltage signal at the PCC point and performing data processing and analysis, injecting the AC voltage component into the output end of the AC / DC interface converter and detecting whether the AC voltage component exists at the converter output end, it is determined whether the distributed power source should stop running.

[0038] The first threshold includes the upper voltage limit Umax and the lower voltage limit Umin; if the voltage at the PCC point is U and satisfies: U > Umax or U < Umin, it is determined that the power supply mode is the island power supply mode, and the island power supply control strategy is selected for execution; if Umin ≤ U ≤ Umax, the output current of the inverter and the voltage signal at the PCC point are collected and decomposed, and through the introduction of the concept of information entropy, the information entropy and wavelet packet decomposition are combined to obtain the feature vector.

[0039] The second threshold includes normalizing the feature vector to obtain a 6D vector as the input of the BP neural network, training and learning in the hidden layer, and finally performing island detection through the output layer; if it is determined that the power supply mode is the island power supply mode, the island power supply control strategy is selected for execution; if it is determined that the island has not occurred, an AC voltage component (with a frequency less than the power frequency) is injected into the output end of the AC / DC interface converter, and then the voltage signal at the output end of the DC / DC converter is sampled to obtain the effective value U' of the AC signal; the effective value U' of the AC signal is compared with the third threshold (the preset voltage value Uset).

[0040] The third threshold includes the preset voltage value Uset; if the effective value U' of the AC signal satisfies: U' < Uset, it is determined that the power supply mode is the island power supply mode, and the island power supply control strategy is selected for execution; if U' > Uset, it is determined that the island has not occurred, and the power supply mode is the mains power network system power supply mode, and the mains power network system power supply control strategy is selected for execution.

[0041] An island detection method based on wavelet packet energy entropy and BP neural network is proposed according to the output current of the inverter and the voltage signal at the PCC point, including: controlling it through an algorithm that combines wavelet packet decomposition and information entropy. The output current of the inverter and the voltage signal at the PCC point are collected and decomposed, and through the introduction of the concept of information entropy, the information entropy and wavelet packet decomposition are combined to obtain the feature vector. The feature vector is normalized to obtain a 6D vector as the input of the BP neural network, trained and learned in the hidden layer, and finally island detection is performed through the output layer. If it is determined that the power supply mode is the island power supply mode, the island power supply control strategy is selected for execution; if it is determined that the island has not occurred, the power supply mode is the mains power network system power supply mode, and the mains power network system power supply control strategy is selected for execution.

[0042] When the DC distribution network is a two-terminal distribution network, it includes two AC / DC interface converters, namely a first AC / DC interface converter and a second AC / DC interface converter; the first AC system is connected to the DC distribution network through the first AC / DC interface converter, and the second AC system is connected to the DC distribution network through the second AC / DC interface converter; the AC voltage component is injected into the output end of the interface converter, specifically including: if it is determined that both of the two interface converters are working normally, the AC voltage component is injected into the output end of any one of the AC / DC interface converters; if it is determined that one of the two interface converters fails, the AC voltage component is injected into the output end of the AC / DC interface converter that is working normally.

[0043] Determining whether an AC / DC interface converter has a fault specifically includes: sampling a second voltage signal at an output end of the AC / DC interface converter; extracting a second effective value of an AC signal in the second voltage signal; comparing the second effective value with a second preset voltage value; and determining that the AC / DC interface converter has a fault when it is determined that the second effective value is less than the second preset voltage value.

[0044] The injected AC voltage component u ac * The expression of u is as follows: ac * =kU dc sin(2πf ac t); where U dc is the rated DC voltage of the DC distribution network; k is the percentage of the injected AC voltage component; f ac is the frequency of the AC voltage component; the value range of k is 2-5%; f ac The first preset voltage value and the second preset voltage value are the same, both of which are Uset, and the value range of Uset is 5% to 20% of kUdc.

[0045] The system of the present invention comprises: a mains network subsystem, other power sources, a distributed power source 1, a distributed power source 2, and a load; the mains network subsystem comprises a first mains power grid system and a second mains power grid system, the first mains power grid system comprises a first power supply G1, a first AC power supply circuit breaker CB11, a first AC transformer T1, a first AC line circuit breaker CB12, a first voltage source converter, and a first DC line circuit breaker CB13 connected in sequence through a distribution line; the second mains power grid system comprises a second backup power supply G2, a second AC power supply circuit breaker CB21, a second AC transformer T2, a second AC line circuit breaker CB22, a second voltage source converter, and a second DC line circuit breaker CB23 connected in sequence through a distribution line;

[0046] The output end of the first AC power circuit breaker CB11 is connected to the output end of the second AC power circuit breaker CB21 through a DC circuit breaker CB7, and the output end of the first AC transformer T1 is connected to the output end of the second AC transformer T2 through a DC circuit breaker CB8; the first DC line circuit breaker CB13 is respectively connected to other power sources, distributed power source 1, distributed power source 2 and loads; the second DC line circuit breaker CB23 is respectively connected to other power sources, distributed power source 1, distributed power source 2 and loads; the load is also respectively connected to the other power sources, distributed power source 1 and distributed power source 2.

[0047] The other power sources include a first branch DC circuit breaker CB1 connected in sequence through a distribution line; the other end of the first branch DC circuit breaker CB1 is respectively connected to the first DC line breaker CB13, the second DC line breaker CB23 and the second branch DC circuit breaker CB2; the distributed power source 1 includes a fourth branch DC converter and a fourth branch DC circuit breaker CB4; one end of the fourth branch DC circuit breaker CB4 is connected to the fourth branch DC converter and the third branch DC circuit breaker CB3 through a distribution line, and the fourth branch DC circuit breaker CB4 is connected to the fourth branch DC converter and the third branch DC circuit breaker CB3 through a distribution line. The other end of the 4-branch DC circuit breaker CB4 is respectively connected to the 1st DC circuit breaker CB13 and the 2nd DC circuit breaker CB23; the distributed power source 2 includes a 6th branch DC circuit breaker CB6 and a 6th branch DC converter; one end of the 6th branch DC circuit breaker CB6 is connected to the 6th branch DC converter and the 5th branch DC circuit breaker CB5 through a distribution line; the other end of the 6th branch DC circuit breaker CB6 is respectively connected to the 1st DC circuit breaker CB13 and the 2nd DC circuit breaker CB23 connection; the load includes other DC loads, local DC load 1 and local DC load 2, the other DC load includes the second branch DC circuit breaker CB2; one end of the second branch DC circuit breaker CB2 is connected to other DC loads through a distribution line; the other end of the second branch DC circuit breaker CB2 is respectively connected to the first DC circuit breaker CB13, the second DC circuit breaker CB23 and the first branch DC circuit breaker CB1; the local DC load 1 includes the third branch DC circuit breaker CB3; the third One end of the branch DC circuit breaker CB3 is connected to the local DC load 1 through the distribution line, and the other end of the third branch DC circuit breaker CB3 is respectively connected to the fourth branch DC circuit breaker CB4 and the fourth branch DC converter; the local DC load 2 includes the fifth branch DC circuit breaker CB5; one end of the fifth branch DC circuit breaker CB5 is connected to the local DC load 2 through the distribution line, and the other end of the fifth branch DC circuit breaker CB5 is respectively connected to the sixth branch DC circuit breaker CB6 and the sixth branch DC converter;

[0048] Example 3

[0049] The control method of the present invention comprises the following steps:

[0050] Step 1: Determine whether an island occurs;

[0051] Step 2: If it is determined that islanding does not occur, the power supply mode is the mains power network system power supply mode, and the mains power network system power supply control strategy is selected to be executed;

[0052] In step 3, if it is determined that an island occurs and the power supply mode is an island power supply mode, an island power supply control strategy is selected for execution.

[0053] The mains network system power supply control strategy includes: when executing the mains network system power supply control strategy, judging whether the first mains network subsystem is operating normally; when the first mains network system is operating normally, controlling the first mains network system to supply power; if the first mains network system fails, detecting the fault location, adjusting the power supply path according to the fault location to avoid the fault location for power supply, including: (1) if it is detected that the fault location is located from the first power supply G1 to the first AC power supply circuit breaker CB11, triggering the first AC power supply circuit breaker CB11 to disconnect, the seventh branch DC circuit breaker CB7 to connect, and controlling the second backup power supply G2 to connect to the first mains network system for power supply; (2) if it is detected that the fault location is located from the first AC power supply G1 to the first AC power supply circuit breaker CB11, If the fault is detected between the first AC power circuit breaker CB11 and the first AC line circuit breaker CB12, the first AC line circuit breaker CB12 is triggered to disconnect, the eighth branch DC circuit breaker CB8 is triggered to connect, and the first power supply G1 is controlled to connect to the second mains power grid system for power supply; (3) If the fault is detected between the first AC power circuit breaker CB11 and the first AC line circuit breaker CB12, the first AC power circuit breaker is triggered to disconnect CB11, and the second mains power grid system is controlled to power supply; (4) If the fault is detected between the first AC line circuit breaker CB12 and the first DC line circuit breaker CB13, the first AC line circuit breaker CB12 is triggered to disconnect, the eighth branch DC circuit breaker CB8 is connected, and the first power supply G1 is controlled to connect to the second mains power grid system for power supply.

[0054] The power supply control strategy of the mains network system also includes: if the first mains network system fails, the distributed power source 1, the distributed power source 2 and other power sources are controlled to supply power to the load until the adjustment of the power supply path is completed.

[0055] The island power supply control strategy includes: detecting whether the total power of distributed power source 1, distributed power source 2 and other power sources meets the load demand. If so, distributed power source 1, distributed power source 2 and other power sources are controlled to supply power to the load. If not, distributed power source 1, distributed power source 2 and other power sources are controlled to supply power to the satisfied load.

[0056] The above are only specific embodiments of the present invention, but the protection scope of this application is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in this application, which should be included in the protection scope of this application. Therefore, the protection scope of this application should be based on the protection scope of the claims.

Claims

1. A method for detecting anti-islanding in a DC distribution network, characterized in that: A three-level judgment is used to determine whether the DC distribution network is in an island operation state, including: sampling the inverter output current and the voltage at the PCC point; comparing the voltage at the PCC point with the set first threshold: if the voltage at the PCC point meets the first threshold, it is determined that the power supply mode is an island power supply mode, otherwise, the wavelet packet energy entropy and BP neural network are used for detection according to the inverter output current and the voltage signal at the PCC point; if the power supply mode is determined to be an island power supply mode, the island power supply control strategy is selected to be executed; otherwise, an AC voltage component is injected into the output end of the AC / DC interface converter, and the voltage signal at the output end of the DC / DC converter is sampled to obtain the effective value of the AC signal; the effective value of the AC signal is compared with the third threshold: if the effective value of the AC signal is less than the preset voltage value, it is determined that the power supply mode is an island power supply mode; otherwise, it is determined that the island does not occur; The first threshold includes an upper voltage limit U max And the voltage lower limit U min ; If the voltage U at the PCC point satisfies: U>U max or U<U min , then the power supply mode is determined to be the island power supply mode, and the island power supply control strategy is selected to be executed; U min ≤U≤U max , then the output current of the inverter and the voltage signal at the PCC point are collected and decomposed, and the concept of information entropy is introduced to combine information entropy and wavelet packet decomposition to obtain the feature vector; The third threshold is a preset voltage value U set , if the effective value of the AC signal U' satisfies: U'<U set , then the power supply mode is determined to be the island power supply mode, and the island power supply control strategy is selected to execute. If U'>U set , it is determined that islanding has not occurred, the power supply mode is the mains power network system power supply mode, and the mains power network system power supply control strategy is selected to execute; The island detection steps using wavelet packet energy entropy and BP neural network according to the inverter output current and the voltage signal at the PCC point include: controlling it by an algorithm combining wavelet packet decomposition and information entropy, collecting and decomposing the inverter output current and the voltage signal at the PCC point, introducing the concept of information entropy, combining information entropy and wavelet packet decomposition to obtain a feature vector; normalizing the feature vector to obtain a 6-dimensional vector as the input of the BP neural network, training and learning in the hidden layer, and finally making an island judgment through the output layer; if it is determined that the power supply mode is an island power supply mode, selecting to execute the island power supply control strategy; if it is determined that the island does not occur, the power supply mode is the mains network system power supply mode, and selecting to execute the mains network system power supply control strategy; When the DC distribution network is a two-terminal distribution network, it includes two AC / DC interface converters, namely a first AC / DC interface converter and a second AC / DC interface converter; the first AC system is connected to the DC distribution network through the first AC / DC interface converter, and the second AC system is connected to the DC distribution network through the second AC / DC interface converter; Injecting an AC voltage component into the output end of the interface converter specifically includes: if it is determined that both interface converters are working normally, injecting an AC voltage component into the output end of any one of the AC / DC interface converters; if it is determined that one of the two interface converters is faulty, injecting an AC voltage component into the output end of a normally working AC / DC interface converter; The method for determining whether an AC / DC interface converter has a fault is as follows: sampling a second voltage signal at an output end of the AC / DC interface converter; extracting a second effective value of an AC signal in the second voltage signal; comparing the second effective value with a second preset voltage value; and determining that the AC / DC interface converter has a fault when the second effective value is less than the second preset voltage value; The injected AC voltage component u ac The expression of * is as follows: ac *=kU dc sin(2πf ac t); Among them, U dc is the rated DC voltage of the DC distribution network; k is the percentage of the injected AC voltage component; f ac is the frequency of the AC voltage component; the value range of k is 2-5%; f ac The first preset voltage value and the second preset voltage value are the same as U set , U set The value range is kU dc 5-20% of the total.

2. An anti-islanding detection system for a DC distribution network, characterized in that: The system uses an anti-islanding detection method for a DC distribution network as claimed in claim 1, and the system includes a mains network subsystem, other power supplies, a distributed power supply 1, a distributed power supply 2 and a load; the mains network subsystem includes a first mains power grid system and a second mains power grid system, the first mains power grid system includes a first power supply G1, a first AC power supply circuit breaker CB11, a first AC transformer T1, a first AC line circuit breaker CB12, a first voltage source converter and a first DC line circuit breaker CB13 connected in sequence through a distribution line; the second mains power grid system includes a second backup power supply G2, a second AC power supply circuit breaker CB21, a second AC transformer T2, a second AC line circuit breaker CB22, a second voltage source converter and a second DC line circuit breaker CB23 connected in sequence through a distribution line; The output end of the first AC power circuit breaker CB11 is connected to the output end of the second AC power circuit breaker CB21 through a DC circuit breaker CB7, and the output end of the first AC transformer T1 is connected to the output end of the second AC transformer T2 through a DC circuit breaker CB8; the first DC circuit breaker CB13 is connected to other power sources, distributed power source 1, distributed power source 2 and loads respectively; the second DC circuit breaker CB23 is connected to other power sources, distributed power source 1, distributed power source 2 and loads respectively; the load is also connected to the other power sources, distributed power source 1 and distributed power source 2 respectively; The other power sources include a first branch DC circuit breaker CB1 connected in sequence through a distribution line; the other end of the first branch DC circuit breaker CB1 is respectively connected to the first DC line breaker CB13, the second DC line breaker CB23 and the second branch DC circuit breaker CB2; the distributed power source 1 includes a fourth branch DC converter and a fourth branch DC circuit breaker CB4; one end of the fourth branch DC circuit breaker CB4 is connected to the fourth branch DC converter and the third branch DC circuit breaker CB3 through a distribution line, The other end of the fourth branch DC circuit breaker CB4 is connected to the first DC circuit breaker CB13 and the second DC circuit breaker CB23 respectively; the distributed power source 2 includes a sixth branch DC circuit breaker CB6 and a sixth branch DC converter; one end of the sixth branch DC circuit breaker CB6 is connected to the sixth branch DC converter and the fifth branch DC circuit breaker CB5 through a distribution line; the other end of the sixth branch DC circuit breaker CB6 is connected to the first DC circuit breaker CB13 and the second DC circuit breaker CB2 3 connection; the load includes other DC loads, local DC load 1 and local DC load 2, the other DC load includes the second branch DC circuit breaker CB2; one end of the second branch DC circuit breaker CB2 is connected to other DC loads through a distribution line; the other end of the second branch DC circuit breaker CB2 is respectively connected to the first DC circuit breaker CB13, the second DC circuit breaker CB23 and the first branch DC circuit breaker CB1; the local DC load 1 includes the third branch DC circuit breaker CB3; the first One end of the 3-branch DC circuit breaker CB3 is connected to the local DC load 1 through a distribution line, and the other end of the 3-branch DC circuit breaker CB3 is respectively connected to the 4-branch DC circuit breaker CB4 and the 4-branch DC converter; the local DC load 2 includes the 5th branch DC circuit breaker CB5; one end of the 5th branch DC circuit breaker CB5 is connected to the local DC load 2 through a distribution line, and the other end of the 5th branch DC circuit breaker CB5 is respectively connected to the 6th branch DC circuit breaker CB6 and the 6th branch DC converter.

3. A method for preventing islanding in a DC distribution network, characterized in that: The method is applied to an anti-islanding detection system for a DC distribution network as claimed in claim 2, and the method comprises the following steps: Step 1: Determine whether an island occurs; Step 2: If it is determined that islanding does not occur, the power supply mode is the mains power network system power supply mode, and the mains power network system power supply control strategy is selected to be executed; Step 3: If it is determined that an island occurs, the power supply mode is an island power supply mode, and an island power supply control strategy is selected to be executed; The power supply control strategy of the mains network system includes: when executing the power supply control strategy of the mains network system, judging whether the first mains network subsystem is operating normally; when the first mains network system is operating normally, controlling the first mains network system to supply power; if the first mains network system fails, detecting the fault location, adjusting the power supply path according to the fault location, so as to avoid the fault location for power supply, including: (1) if it is detected that the fault location is located from the first power supply G1 to the first AC power supply circuit breaker CB11, triggering the first AC power supply circuit breaker CB11 to disconnect, the seventh branch DC circuit breaker CB7 to connect, and controlling the second backup power supply G2 to connect to the first mains network system for power supply; (2) if it is detected that the fault location is located from the first AC power supply circuit breaker CB11 to the first AC line breaker CB12, the first AC line breaker CB12 is triggered to disconnect, the eighth branch DC breaker CB8 is triggered to connect, and the first power supply G1 is controlled to connect to the second mains power grid system for power supply; (3) If the fault location is detected between the first AC power supply breaker CB11 and the first AC line breaker CB12, the first AC power supply breaker is triggered to disconnect CB11, and the second mains power grid system is controlled to supply power; (4) If the fault location is detected between the first AC line breaker CB12 and the first DC line breaker CB13, the first AC line breaker CB12 is triggered to disconnect, the eighth branch DC breaker CB8 is connected, and the first power supply G1 is controlled to connect to the second mains power grid system for power supply; The power supply control strategy of the mains power network system also includes: if the first mains power grid system fails, controlling the distributed power source 1, the distributed power source 2 and other power sources to supply power to the load until the adjustment of the power supply path is completed; The island power supply control strategy includes: detecting whether the total power of distributed power source 1, distributed power source 2 and other power sources meets the load demand; if so, controlling distributed power source 1, distributed power source 2 and other power sources to supply power to the load; if not, controlling distributed power source 1, distributed power source 2 and other power sources to supply power to the satisfied load.

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